No documentation yet, but the pin-layout is in the source, and the floppy connector is a standard.

Command set:

DI[01], Direction in or out
DS[01], Drive Select on or off
Hx[01], Head Load off or on
I List input signals and current track
M[01], Motor off or on
P[01], Head movement patterns; 0 = Track00 to trackCount and back, 1 = random between Track00 and trackCount.*
R, Reset all signals (to 1)
SKnn, Seek track (always two decimal digits)*
SR, Measures the rotation speed in RPM*
SS[01], Side Select 0 or 1
STnn, Execute steps (always two decimal digits)
Tnn, Number of tracks (always two decimal digits). Default is 35.
? Short help
*) these commands start and stop the drive (DS0 & M0 resp. DS1 M1).

The FDDexer Arduino sketch is released under the 3-clause BSD license. So instead of asking me to add a
feature, you could add it yourself :-).